1. Field of the Invention
The present invention relates to a board-mounted type connector to which a shield plate is attached. The present invention particularly relates to a connector mounted on a plug-in type circuit board housed in large numbers in an optical transmission system or other large-scale control system and the structure of a shield plate attached between this connector and circuit board.
2. Description of the Related Art
In recent years, the means for transmission of telephone and Internet information has been shifting from electrical signals to optical signals. An optical transmission system converts as input optical signal to an electrical signal, then amplifies it and reconverts it to an optical signal for transmission to a remote base station. An optical transmission system houses a large number of circuit boards, on which electrical devices are mounted, in the form of plug-in units able to be plugged into the system frame by connectors.
A plug-in unit is configured by mounting ICs forming control circuits or other electronic circuit parts on a circuit board by automatic insertion or another means, then mounting the connectors and electrically connecting them by solder etc. The connectors mounted on a circuit board include an optical connector which receives optical signals and convert them to electrical signals for transfer to the circuits on the circuit board and an electrical connector which transfer electrical signals on the circuit board to other plug-in units in the system (hereinafter, electrical connectors simply referred to as “connectors”).
A connector connects a plug-in unit to a connector provided on the frame. Usually, the frame side connector is a male connector, while the plug-in unit side is a female connector. Further, as explained above, a connector transfers electrical signals on the circuit board to another plug-in unit in the system. It is plugged into a male connector provided on the frame, so usually is mounted on an end of the circuit board and fastened by solder.
A plurality of plug-in units are housed in an optical transmission system. Each plug-in unit is comprised of a circuit board on which a connector and optical connector are provided. The connector is connected to a connector provided on the frame of the optical transmission system. A plurality of plug-in units are housed in the frame oriented in the vertical direction. The sections housing the plug-in units are called “shelves”.
The circuit board of each plug-in unit mounts electronic devices including a large number of integrated circuits (LSIs and ICs) forming electronic circuits. Further, one end of the circuit board has a connector attached to it, while the opposite end has an optical connector attached to it. A connector often has a shield plate attached to it covering the top surface and back surface of the connector.
A connector requires a shield plate in general to shield adjoining transmission paths and prevent adjoining transmission paths from affecting each other or to prevent an outside electromagnetic waves from being received at a terminal of the connector and unnecessary signals from entering a transmission path in a connector performing high speed transmission of electrical signals. There have been various configurations of shield plates in the past. For example, as a shield plate designed to prevent adjoining transmission paths from affecting each other, FIG. 1 of Japanese Patent Publication (A) No. 2002-231390 discloses ones shielding adjoining connection terminals (contacts). Further, in the shielded connector assembly described in this prior art patent, the contacts as a whole are covered by a metal rear shell.
The back surface of a circuit board of a plug-in unit usually is not provided with any electronic devices. On the other hand, the connector provided at an end of a circuit board is attached from the front surface of the circuit board. Therefore, the mounting pins of the connector to the connector stick out from the rear side of the circuit board. Accordingly, the rear side of the circuit board has a shield plate attached to it to shield the mounting pins of the connector. Here, the structure of a connector attached to a circuit board and a shield plate attached between a connector and rear surface of a circuit board for shielding the mounting pins of the connector will be explained.
The case of a board-mounted type connector attached from the front surface of a circuit board where electronic devices are mounted will be explained. A connector has an insulating housing. This insulating housing has a board mounting surface, step difference surface, shield plate engagement surface, male connector connection surface, two side surfaces, a top surface, and a back surface.
The board mounting surface is provided with metal pins, sticking out from it in a dot matrix, for passing through a large number of mounting holes provided at an end of the top of the circuit board. The mounting holes have not shown circuit patterns connected to them. The step difference surface is perpendicular to this board mounting surface and has a height (step difference) of at least a thickness of the circuit board. The shield plate engagement surface adjoins the step difference surface and is formed parallel to the board mounting surface. When the shield plate engagement surface has a tapered surface inclined toward the male connector connection surface side, the step difference part formed at a terminal end of the tapered surface is provided with engagement holes running through the male connector connection surface side. The male connector connection surface is a surface parallel to the step difference surface and is provided with the same number of openings as the metal pins. The openings are provided deep inside them with female connector parts for electrical connection with the metal pins.
The shield plate attached between the shield plate engagement surface of a connector and the circuit board after this connector is attached to the circuit board is made of metal and is provided with an engagement part to be engaged with a shield plate engagement surface of a connector, a shield part for shielding metal pins sticking out from the circuit board, and a mounting part provided with press-fit pins fastened by insertion into engagement holes provided in the circuit board.
The engagement part has a smaller thickness. Engagement tabs for insertion into engagement holes running from the shield plate engagement surface side of the connector to the male connector connection surface are provided at a free end of the engagement part. The distance between engagement tabs is equal to the distance between engagement holes. Further, the engagement part is provided at its center part with a plurality of holes for lightening the weight of the connector and securing flexibility of the engagement part. The tapered surface of the connector may also be provided with projections corresponding to these holes. Further, instead of the tapered surface, the shield plate engagement surface may also be provided with a simple recess.
The shield part is a flat plate with a large thickness and is provided with an area covering the metal pins sticking out from the circuit board. The mounting part is provided perpendicular to the shield part. The free end side is provided with press-fit pins at predetermined distances. The press-fit pins have sharp free end parts, but the parts following the free end parts are formed as bulging parts. These bulging parts have widths larger than the diameters of the engagement holes provided in the circuit board. Due to the bulging parts, the press-fit pins can be fastened in the engagement holes.
When attaching the shield plate between the connector and circuit board, first the engagement tabs of the free end part of the engagement part of the shield plate are passed through the engagement holes running from the shield plate engagement surface side to the male connector connection surface, then the press-fit pins provided at the end of the mounting part are inserted into the engagement holes provided in the circuit board.
When inserting the engagement tabs of the free end part of the shield plate in the engagement holes, then press-fitting the press-fit pins provided at the free end side of the mounting part into the engagement holes, the pushing jig is positioned above the press-fit pins of the shield plate and the press-fit pins are pushed by the pushing jig.
However, in the prior art, in the state with the free end part of a press-fit pin provisionally inserted into an engagement hole, there was a deviation (difference in angle) between the axial line of the press-fit pin and the axial line (vertical to the circuit board) of the engagement hole (the engagement hole being a through hole copper plated on the part on the circuit board and the inside circumference). That is, the axial line of the press-fit pin is not vertical to the circuit board, so if vertical direction force is applied all at once in this state, the force will disperse resulting in deformation of the shield plate or force being applied rotating the press-fit pin while the press-fit pin is inserted into the engagement hole, so the press-fit pin will buckle or other press-fit defects will occur and a problem will arise in quality.
As a method for press-fitting press-fit pins into engagement holes so that this problem does not occur, there is the method of dividing the pressing action against the press-fit pins 44 into several actions to disperse the pushing force, but with this method, there are the problems that the time for press-fitting the press-fit pins in the engagement holes becomes longer and the number of circuit boards produced per unit time ends up being reduced.